Noise-immune synchronizing-signal separator for television receivers



FOR TELEVISION RECEIVERS Original Filed July 21, 1950 moimwzmw a I l I l I I l l I I I I I I I I I I I I I I I I I J lP i-rn r It I u H m 524%? finin 5; "if 553mm. "655% ozw3uE 524262 5233i 86; a 25552 192.363 29E a 8. 2 I: r; 2 55524 W. QZmQGwEQ zz wazno Iii United States Patent O NOISE-llVllVIUNE SYNCHRONIZlNG-SIGNAL SEPA- RATOR FOR TELEVISION RECEIVERS Donald Richman, Fresh Meadows, N.Y., assignorjo Hazeltine Research, Inc., Chicago, 111., a corporation "of Illinois Original application July 21, 1950, Serial No. 175,192. Divided and this application December 23, 1957, Serial No. 704,663

Claims. (Cl. 178-73) General The present invention relates to control or noisesuppression apparatus for use in television receivers and is especially directed to synchronizing-signal separating apparatus having improved immunity to undesired noise present in an applied composite video-frequency signal.

Although the invention is particularly suited for use as a synchronizing-signal separating apparatus, it also has utility for automatically controlling an operating characteristic of a television receiver such as the gain or amplification thereof.

This application is a division of application Serial No. 175,192, filed July 21, 1950, now abandoned.

In accordance with present television practice, there is developed and transmitted a signal which comprises a carrier wave modulated during recurrent intervals or trace periods by picture components representative of the light and shade values of an image being transmitted. During retrace intervals between the trace periods, the carrier wave is modulated by synchronizing-signal components or pulses which correspond to the initiation of successive lines and fields in the scanning of the image being televised. At the receiver, a beam is so deflected as to scan and illuminate the target of a cathode-ray image-reproducing device in a series of fields of parallel lines and the picture components of the received signal are utilized to control the intensity of the scanning beam. The linescanning and the field-scanning components of the received signal are separated from the picture components and from each other and are utilized to synchronize the operation of the receiver line-scanning and fieldscanning generators with the similar scanning apparatus utilized at the transmitter in developing the transmitted signal. The transmitted image is thereby reconstructed on the target of the receiver.

Since negative modulation of a television carrier-wave signal is standard practice in the United States, the amplitude or intensity of the received carrier-wave signal is a maximum during the occurrence of synchronizing-signal components and undesired high-amplitude noise.

Synchronizing systems of television receivers are particularly sensitive to high-amplitude noise interference which impairs the operation of the receiver scanning genverators. It is highly important that the synchronization of both the line-scanning and the field-scanning generators of such a receiver be accomplished with precision in order that proper scanning may be obtained. It is particularly significant that synchronization of the line- "ice faulty scanning. operates at a relatively low frequency and is controlled by pulses of long duration, it is less susceptible than the line-scanning generator to noise disturbances of the type under consideration. However, accurate synchronization of the last-mentioned generator is nevertheless important in a television receiver.

In view of the well-known susceptibility of the scanning systems of television receivers to noise disturbances, some such receivers have utilized synchronizing-signal separating apparatus which are substantially blocked against undesired disturbances during a portion of each operating cycle. Although synchronizing-signal separating apparatus of this type has been found to be generally satisfactory, the circuits thereof have often required the use of time delay networks and other circuit components which render the apparatus relatively complex and, hence, more expensive to manufacture than is desirable for many applications.

It is also desirable that a television receiver include suitable apparatus for developing a control effect automatically to control an operating characteristic thereof, such as the gain or amplification. It is desirable that this gain-control effect, usually referred to as an A.G.C. effect, be determined by the intensity of the incoming signal, that is, the intensity of the carrier-wave signal, and be substantially independent of its picture-modulation components. Furthermore, it is especially desirable that the automatic-gain-control apparatus, like the synchronizing-signal separating apparatus, exhibit a high immunity to noise of the sort mentioned above. Automatic-gain-control apparatus of this type is capable of developing an automatic-gain-control effect which, in turn, is effective very accurately to maintain the signal input to the various stages of the receiver within a relatively narrow range for a wide range of received signal intensities.

An automatic-gain-control apparatus of the type just mentioned, Which is keyed into operation only during the occurrence of the line-synchronizing pulses and which is effectiveto reject undesired interference such as noise, is disclosed and claimed in United States Letters Patent No. 2,547,648, granted April 3, 1951, and entitled Automatic-Contrast-Control System for Television Apparatus. Such apparatus is becoming very Widely employed in television receivers. Manifestly, it would be desirable to obtain from a simple synchronizing-signal separating apparatus which apparatus is relatively immune to noise not only a desired synchronizing signal but also an automatic-gain-control eiiect similar to that derived by apparatus in accordance with the above-identified patent.

Furthermore, it is desirable that the gain-control effect be substantially unresponsive to those high-amplitude noise impulses which may be superimposed on the synchronizing-signal pulses.

It is an object of the invention, therefore, to provide for use in a television receiver a new and improved synchronizing-signal separating apparatus which avoids one or more of the disadvantages of prior such apparatus.

It is another object of the invention to provide for use in a television receiver a new and improved synchronizingsignal separating apparatus which is simple in construc- 'tion, inexpensive to manufacture, and yet is capable of providing excellent rejection of interference such as highamplitude random or impulse noise.

It is yet another object of the present invention to provide for use in a television receiver a control apparatus which is effective to derive substantially noisefree synchronizing signals having an amplitude relatively independent of amplitude variations of the applied composite video-frequency signal and which is also effective simultaneously to derive an automatic-gain-control eflect Since the field-frequency generator.

p ia e nutin t ap en c 7 vice.

together with other and further objects thereof, reference is hacltothe following description taken in connection with the accompanying draWing and its scope will be Theaccompanying drawing, 5g. 1, is a c ircuit diagram, partly schematic, of a complete television receiver ineluding an automatic-control apparatus in accordance with a particular form of the invention.

'iiial description (if Fig. 1 receiver 1 now more particularly to Fig. 'l of the draw- :ing, the; television 'receiver there represented comprises a ;receiver of the superheterodyne type including an antenna system 10, 11 coupled to a radio-frequency amplifierlZ or: one or more stages. There are coupled to the latterunit in cascade, in the order named, an oscillator .-inedulator 1 3, an intermedate-trequency amplifier 14 of one or more stages, a detector 15, a direct-current ,r deorf equencr ampl fi r 1 of or mo ,v a

a cathode-ray irnage eproducing device 17 of conventionalcpnstrugtion provided with the usual line-frequency and field frequency scanning coils for deflecting the cathode-ray beam ;in two directions normal to each other. Connected tothe output terminals of the intermediate- Irequencyamplifier 14 is a conventional sound-signal de: tector and amplifier 18 which comprises the usual frequency detector, amplifiers, and sound-reproducing de- An output circuit of the video-frequency amplifier 16 cqupledto an input circuit including input terminals 25,26 of a control'apparatus 1?, and an output circuit ofthe latter, including output terminals 27, 27, is conpledto a linescanninggener'ator 21 and a field-scanning generator through an intersyncihronizing-si-gnal separator 20. The-output circuit of the generator 21 is conpld in a conventional manner to the line-scanning coil of theimage-reproducing device 17 through a line-scanning' amplifier 23 while the field-scanning generator 22,

may include suitable amplifiers, is connected to the field-scanning coil of the image-reproducing device. outputcircuit of the line-scanning amplifier 23 is Eormected to input terminals 29 29 of the control apparaare 19. Outpiit terminalsZS, 28 of the control apparafor. a et r nde stan i s q it Pr e n ntion 7 eontrol supply in the unit 19, is applied by -the control circuit conductor as an automatic-amplificaion-contiol bias to the gain-control circuits of units 12, 13, and 14 to maintain the signal input within a relatively narrow range for a wide range of received signal intensities. The unit 19 also selects the synchronizing signals from the othiei' modulation components of the. composite videofrequency signal applied thereto by the video-frequency amplifier 16. t 7 i r a r The line-synchronizing and field-synchronizing signals derived by the unit 19 are applied by the terminals 27-, 27 to the intersynchronizing-signal separator 20 wherein the are separated from each other and are then supplied to individual ones 'of the'generators 21 and 22 tosynand field-fre uency generators '21 and 22, res esavery.

The output signal of the generator 21' is supplied to tlfe line scann'ing coil of-unit 17 through the amplifier 23 while the output signal of generator 22 is supplied direct- 19 are connected to the input circuits of one or more of thestages of the units 12, 13, and 14 by a control circiiit conductor 25 to supply an automatic-gain-control srnoo. effect to those stages. The units 16-23, in-

"clu'sive, with the exception of the apparatus 19 which is ob'nstru'cted in accordance with the present invention and be described in detail hereinafter, may be of con- 'ntional construction and operation so that a detailed a sen uenand explanation of the operation thereof are unnecessary herein.

General operation of Fig. 1 receiver supplied to the oscillator-modulator 13 wherein they are converted into intermediate-frequency signals.

I The latter, in turnqare selectively amplified in the intermediatef eqitene amplifier 14 and are delivered to the detector 15. The modulation components of the signal are derived by the detector '15 and are applied to the directcu'rr en't video-frequency amplifier 16 wherein those components including the original unidirectional components 'i'e amplified and from which they are supplied to the input circuit of the image-reproducing device 17.

; A control voltage, which is derived in a manner to be "e p aided in detail subsiequently by an automatic-gainly to the field-scanning coil ofdevice -17 to produce the usual scanning fields, thereby to deflect the catho beam of device 17 in two directions normal'to each other to trace a rectilinear scanning pattern on the screen of the tube and thereby reconstruct the translated pictuie.

The audio frequency modulation components of the received signal are derived in a conventional manner by the sound-signal detector and amplifier 18 and are applied to the loudspeaker thereof and converted to sound.

Description of control apparatus of F ig. 1

Referring now more particularly to Fig. 1 of the drawing, the automatic-control apparatus "19 for the television and hence appears in series-relation With'the space-current path of the tube. This network comprises an energystorage devic'etin the'forin of a condenser 33 which is connected in parallel with a pair of series-connected resistors 34fan'd 35. The resistor 35 is adjustable for controlling the magnitude of the cathode bias of the tube 30 and the contrast of the image reproduced by image-reproducing device 17 of the television receiver in a manner which will be described subsequently. A source of unidirectional potential indicated as +B is connected to the cathode of the tube 30 through a voltage divider including a resistor 60 and the resistors 34 and 35 for tie veloping a suitable bias on the cathode of the tube. The

network 32 preferably has a time constant which is at least several times the period of the line-synchronizing signal components applied to the input terminal 26, 26 of unit l9. I r

The apparatus19 further includes a supply circuit comprising means coupled to the input electrodes of the tube 30 including the control electrode thereof for a plying thereto the video-frequency signal derived by the detector 15, the amplitude of which signal may vary and which elfectively includes picture components, black-level pedestals, at least'one type of synchronizing-signal components, namely the line-synchronizing signal components, and the original unidirectional or direct-current components representative of light variations and which may include undesired random pulses at least someof which may have anamplitude greater than the amplitude of the synchronizingignal components. The linesynchronizing signal components are more positive than the picture components and tend to convert the tube 30 from one of its operating conditions to another." The means just mentioned comprises the input terminals '26, 26 which are connected to the input circuit of the videofrequency amplifier 16 and also comprises a currentlimiting resistor 37 connected between one of the ter- 'minals and the control electrode of tube 30.

The apparatus also includes a source of a control signal having an amplitude substantially unaffected by amplitude variations of the synchronizing-signal components derived by the receiver for supplying the aforesaid control signal to one of the electrodes of the tube 30, specifically to the anode thereof, in synchronous relation with the application of the line-synchronizing signal components to the control electrode and with such polarity as to convert the tube from one operating condition to another substantially only during the intervals of the line-synchronizing signal components, thereby to develop across the network 32, in a manner to be explained subsequently, a control effect related to the peak amplitude of the line-synchronizing signal components but} substantially independent of the accompanying unjdesiredrandom pulses. This control-signal source comprises an input circuit including the input terminals 29,

. 29 which are coupled to an output circuit by the line- -scanning amplifier 23 and to the tube 30-through a coupling condenser 39. A condenser 40 is connected between the anode of the tube 30 and-ground and efiectiv'ely constitutes the input impedance of that circuit. The highpotential one of the terminals 29, 29 is preferably coupled to a suitable point in the line-scanning amplifier 23 such as the anode of the amplifier tube where there is 'coupled, in a conventional manner during each line-re- "trace interval, a relatively high-amplitude, short-duration impulse of positive polarity due to the collapsing mag ne tic field in the circuits associated with the line-scanning coil of the image-reproducing device 17. The well-known characteristics, such as the Q of the tuned circuits of the generator 21 and its amplifier 23, are such that the positive output pulse applied to the terminals 29, 29 has an amplitude which is substantially unaffected by amplitude variations or temporary loss of the synchronizingsignal components applied to the terminals 26, 26 of unit 19 from the video-frequency amplifier 16.

In accordance with a feature of the invention fully described and explained in Patent No. 2,784,249, granted March 5, 1957, and entitled Keyed Automatic Gain Contro a condenser 80 which is represented in brokenline construction since it may be comprised in whole or in part of the anode control-electrode capacitance of the tube 30 and the inherent capacitance of the connections to those electrodes, is connected between the anode and the cathode of the tube.

i The control apparatus 19 additionally includes a parallel-connected resistor 48 and condenser 47 forming -a second impedance network 45 which, like the network 32, ;has developed thereacross a control potential having a 'value proportional to the cathode current of the tube 30 and related to the peak amplitudes of the line-synchroniz- -ing signal components but substantially independent of :the undesired random pulses. One terminal of the network 45 is coupled to the anode of the tube 30 through a resistor 46 while the other terminal thereof is connected "to a point of fixed reference potential such as ground. The network 45 and the resistor 46 constitute a direct- 'current path between the anode of the tube 30 and 'ground. The junction of the network 45 and the resistor 46 is connected to the automatic-gain-control output terminals 28, 28 of the unit 19. The network 45 is preferably proportioned to have a time constant at least several times the interval between the line-synchronizing pulses. The operating potentials developed and applied to the ftube 30, in particular that developed across'the network 32, are such that it is normally nonconductive.

The unit 19 also includes'a utilization circuit or-syn- 6 chro'nizing' signal' stripper'means including an electron discharge device coupled to the applying means comprising the high-potential one of the terminals 26, 26 and to the network 32 and responsive to at least some of the various components of the applied video-frequency signal for deriving synchronizing-signal components which are'substantially independent of the undesired random pulses and which have amplitudes substantially independent of any amplitude variations of the video-frequency signals applied to the terminals 26, 26, This device comprises a rectifier device in the form of a triode 50. The control electrodes of the tubes 30 and 50 are interconnected through a resistor 61 and the anode of the tube 50 is connected to a source of potential +B through a load resistor 51 and is also connected to the high-potential one of the output terminals 27,27. A positive bias potential, which is effective normally to maintain the tube "50 in a nonconductive condition, is applied to the cathode 'of, that tube through a resistor 43 which has one terminal thereof connectedto the junction of resistors 63 and 64 which are connected in series between the cathode of the tube30 and ground. The resistors 63 and 64 preferably :have a resistance which is much greater than that of either ofthe resistors 34 or 35.

The apparatus 19.,additionally includes a resistive impedance network 65 which is coupled to the network 32 -and is responsive to the control potential developed in network 32, this impedance network 65 having parameters so proportioned as to develop between the highpotential or ungrounded one of the terminals 26, 26 and a predetermined portion of the network 65 a unidirectional potential having an amplitude less than that of the pedestals of the modulation signal applied to the terminals 26, 26 and. which varies in a manner approximately directly proportional to variations in the amplitude of the predetermined shade or black-level pedestals or of the'synchronizing signal components but which is substantially. independent of the aforesaid undesired random pulses. vThe impedance network 65 comprises 'f'a potential divider including a pair of series-connected resistors 67 and 68 connected across resistor 35 through an adjustable tap 70 of a voltage divider 71 connected to a source indicated +B, this divider serving to control background intensity or brightness of the image produced by the image-reproducing device 17 of the receiver. The junction of the resistors 67 and 68 is connected to an output terminal 72 which is, in turn, connected to the control electrode of the image-reproducing device 17. Each of the resistors 67 and 68 has arvalue of resistance much greater than that of the contrast control 35 and also greater than that of the resistor 71, particularly that portion of the latter between the tap 70 and ground. The details of the proportioning'of the impedance network 65 are more fully explainedin connectionwith Fig, 1 of Patent 2,673,892, granted March 30, 1954, and entitled Automatic-Control Apparatus for Television Receiver."

The apparatus 19 further includes a control circuit including a circuit element in the form of a rectifier device 90 coupled hetween the applying means, or the high-potential one of the terminals 26, 26, and the impedance network 32 'andhaving a threshold response and, above the threshold, being efiectively responsive jointly to the control potential developed across the network 32 and to those random pulses having an amplitude greater than the amplitude of the synchronizing-signal components foryderiving a control effect of recurrent pulse wave form, individual pulses of which have an device 90, which may: be of the contact or the thermionic type, is connected withsuch polarity that it is efiective 'toeonduct upon'the: application to the terminals 26, 2'6 'oi positive-going noise;pulses having an amplitude greater than that of the linesynchronizingsignal pulses.

m Me a he recan ed; directlyo h l .4 which t5 he. e min s .6.15 nd he Ot s; hereqt-ls. con ec d r tly o h ca h Qf h u s T u the athosiet he' ice 0. s coupled to the impedance network 32 through the re- ,.sistor network 43, 64, '63. Asiwillbe made'clear hereinatter, the tube 50 of the. synchronizing-signal separator comprisesra means forutilizing the control. effect developed by the rectifier device9.0

' Operation of Fig. 1 controlapparatus In consideringrthe operationof the apparatus 19, it

will be assumed initially. that the. proper. operating ,bias

has. been established across the. network 32 by adjustment of the resistor 35 and also by the biases. established across the networks 45 and 32by afew. cycles of operation of the apparatus. As previouslymentioned, it

also be assumed that the 'tube 3i i normally nonconductive and. is effective to conduct only during the occurrence of the lines'ynchronizing pulses. It will befurther apnoea cent-s nc nizing-signal peaks applied to the control 'electrodefof tube. 3% Conversely, when the amplitude of the SW? .chronieing-signal pulses increases, the potential appear ing'across tlne' network 32 increases in proportion to the aforesaid amplitude increase. Consequently, the refer encelevel or potential established at the cathode of the tube 3ti, onthepotential across a portion of the network I 32, varies in accordance with the peak amplitudes of the assumed that. the position on theresistor 71fof thetap V 70 controlling the' lbri'ghtness of; the image. reproduced by thedeviceli' and also that-the. adjustment of the. contrast control cause the device 17.to produce a proper.

image. As hereinbefore mentioned, thecompositevide'ofrequency signal including the usual picture components, the line-synchroniing and field synchronizing components, and the unidirectional components is supplied by the output circuit of the direct current video-frequency amplifier 16 to the terminals 2 6, 26 coupled to the control electrode-cathode input circuit of the tube 30.-

. condenser 39 acoritrol signal comprising periodic positivepolarityi gating pulses. supplied by the line-scanning amplifier. 23. These periodic pulses, which constitute the sole anode.energizing-,potential for the tube.30, are applied to the anode thereof in synchronous relation with, in particular coincident'with, the applicationof the line-synchronizing pulses periodically and momentarily to render the. tube 30 conductive,fthereby to develop across the. network 32, or a portion thereof such as across, resistor 35, a .unid irectional control potential of positive polarity dynamically. related. tothepeak amplitude of. the line-synchronizing components. Specifically, the developed potential is. proportional to the. amplitude of thosecoinponents and is positive at the cathode of the tube 3%). A potential, having a value related .to the aforesaid cathode. potential buthaving. 'a negative polarity atv the junction of theresistors 46 and 48, is developed across the network sincethenetworks 32 and 45 are both in the same direct-current. anode-cathode loop or circuit of the'tube 30.. The potential. developed. across the last-mentioned network for "application to the output terminals 28 28 is related to the. average direct current drawn from the anode excitation source comprising the terminals 29, 29 and this potential, as will be made clear subsequently, constitutes an automatic-gain-control potential related .to the peak value of the composite videofrequency signal appliedtothe.terminals26, 26 Hence,

.to produce some positive. clipping of any. noise pulses having an amplitude equal to or; greater than the synchronizing pulses, The conjoint action on the tube 30 of; the, gatingpulses and-the line synchronining pulses is to establish a vanabledirect-current reference level or positive p n a at e ath e o emb 0, h across thenetwor'k 3.2 'Ihislevel isficttt mi fi b ihg currence of a synchronizing-signal pulse.

- components oi the signal applied to the terminals26,

2.6. This, in turn, keeps the average'aniplitude of: the

potential between thecontrolelectrode and the cathode vatl-a level which bears a substantially fined relationship Ito the level ccn responding to the level of; the synchronizing-signal peaksapplied to the controlrelectrode. of b .0- g a Potential changes corresponding to thoseappearing across the network 32 but of opposite polarity thereto are developed acrossthe network 45. 7 Since. the time constant of the network 4 5 is long with reference to the interval between line-synchronizing pulses, an average potential related to the peak amplitude of the line-synchronizing signal components and, hence, the carrier amplitude, is developed across that network and constitutes an accurate desirable automatic-gain-control potential. a t a a 7 Considering the circuit of. the ,tube30 from a somewhat diiferent standpoint, the circuit may be regarded for direct-current conditions as being in the nature of .a

. cathode-followeramplifier wherein the. potential of the cathodev follows thatof the control electrode; Thus, the average potential of the cathode of thetube 30 bearsa fixed relationship to the instantaneous potential. appearing on the control electrode of that tube during theoc- Expressed somewhat difierently, the composite video-frequency signal applied to the controlelectrode-cathode circuit of the tube 30 efiectively acts in series wtih the 'variablediroot-current reference level established at the cathode of the tube or acrossa selected-portion of the network 32. Thus, the circuit of the tube 30 may be considered to constitute a clamping circuit which is effective to clamp the cathode or a selected point on the network 32 such as the junction of the resistors 34- and 35 to a varying reference. level. The significance of this'feature will be made clear presently. v

The resistor network 63, 64, 43 is efiective to supply a suitable positive bias to'the cathodeof the tube 50, thus effectively determining the magnitude oi the signal required for application between the control electrode and the cathode of the tube 50 to render it conductive. Since the tube 50 performs a clipping function, the bias just mentioned is selected by suitable proportioning of the; resistors 60, 63, and 6 4 and theselection of the potential-+B so that-the clippinglevel i above the maxi mum amplitude level of the picture-signal components of the composite video-frequency signal. When the tube 51 is rendered conductive there is developed at its anode and hence between the terminals 27, 27 only synchronizing-signal components having approximately constant amplitudes for application to the intersynchronizing signal separator 20.

In addition to supplying a synchronizing-signal output signal having an approximately constant amplitude, unit 19 has a low susceptibility to undesired random pulses 911 91 nisi ht t aise r es. rin h ins :tervals between applied linefsynchronizing pulses. Since short-duration positive pulses are applied to the input terminals 29, 29 ofthe unit 19 fromthelline-scanning amplifier 23 to gate or ,key the tube 30, the anode-cathode path through the tube is conductive only for a very small percentage of the time and the resistor 37 so limits the current that can flow from the control electrode to the cathode due to strong noise pulses that the average value of this control-electrode current is normally small in comparison with that of the anode current. Accordingly, random or noise impulses occurring between synchronizing pulses have an inappreciable effect on the operation of the tube 30 and also'on' the variable bias potentials developed across the networks 32 and 45. Conse'quently, the automatic-gain-control portion' of'the unit 19, constitutes a' so-called keyed automatic-gain-control system which is characterized by its excellent noise immunity. Noise impulses having an amplitude greater than the desired synchronizing pulses are reduced by.

grid-current limiting in the circuit including the resistor 37. and, due to the periodic conductivity of the tube 30 at the line-synchronizing signal rate, the reference level developed at the junction of the resistor 34 and the condenser 33 is not appreciably afiected' by high-amplitude 'noise appearing in the signal applied to the terminals 26, 26 of the unit 19.

Ithas been previously stated that the potential developed at the cathode of the tube 30 is related to the tips of the synchronizing pulses. Since the cathodes of the tubes 30 and 50 are interconnected through a resistor network, the potential variations at the cathode of the tube 50 are related to those at the cathode of the tube 30., Random noise pulses which have an amplitude that exceeds the threshold established at the cathode of tube 50 are efiective' to render the rectifier device 90 conductive, thus developing a potential across the load resistors 43 and 64. The device 90 is thus difierentially actuated by the noise pulses and the unidirectional potential de- -veloped at the cathodes of devices 90 and 50. Accord- Y ingly, there is developed at the cathode of the tube 50 from the aforesaid random noise pulses a relatively large Icontrol efiect of recurrent pulse wave form, individual pulses thereof having a positive amplitude related to the amplitude difierence between those random pulses which exceed the peak amplitude of the synchronizing pulses and a direct-current potential derived from those synchronizing pulses. These recurring positive polarity pulses are effective during the occurrence thereof to bias or to maintain the tube 50 at anode-current cutoff, thus materially reducing or effectively minimizing the transllation of random noise pulses to the output circuit of the tube 50 and, hence, to the terminals 27, 27. Due to finite bandwidth limitations of the circuits associated with the tubes 30 and-50, short spikes corresponding'to the lead- ;ingand the trailing edges 'of the random no'ise'pulses may be translated from the terminals 26, '26 through the aforesaid tubes to the synchronizing-signal output terminals 27, 27. Due to stray circuit capacitance, howfever, these spikes are materially reduced in amplitude fto a value much lower than that of the original noise pulses. From the foregoing description and explanation it will be seen'that the circuits of the tube 50 and the rectifier jdevice 90 comprise asynchronizing-signal translating sys tem including an input circuit (the input'circuit of' the tube 50) coupled between'the applying means comprising the ungrounded one of the terminals 26, 26 and the network 32 and responsive to the control potential developed in the network 32 and to themodulatiou signal and also including an output circuit (comprising the output circuit of the tube 50), the circuit elements of this translating system :being arranged to develop a control effect in the input circuit (namely, the periodic potential 'pulses applied to the cathode of tube'50) fromrthe ranarrests The condenser and the primarily resistive impedance I of the control electrode-cathode input circuitof the tube 30 comprise a differentiating means which is effective to render the potential developed across the networks 32 and 45 substantially unresponsive tov relative phase variations between the signal appliedto the anode of the tube 30 and the signal applied to the control electrode of that tube in a manner fully explained in Patent No. 2,784,249. 'In the manner fully explained in Patent No. 2,67 3,892, the network 65 develops for application to the control electrode of the image-reproducing device 17 a potential which varies in accordance with the pedestals or black level of the composite video-frequency signal applied to the acthode-ray device, thus assuring that the device 17 reproduces all picture components with the correct shade so that light gradations from black to'white are properly reproduced in'the reproduced image." -While applicant does' not intend to limit the'invention .to'any specific circuit constants,'the following constants are given as illustrative 'of oneembodiment of theinvention constructed in accordance with the apparatus of Fig. 1: a

Resistors 34 and 46 150 kilohms. n V V Resistor 35 250 kilohms (mam).

Resistor 37 10 kilohms.

Resistor 43 47 kilohms.

Resistor 48 100 kilohms (max.).

Resistor 51 220 kilohms.

Resistor 60 390 kilohms.

Resistor 61 22 kilohms.

Resistor 63 15 kilohms.

Resistor 64 390 kilohms.

Resistor 67 1.5 megohms.

Resistor 70 320 kilohms (max).

Condenser 33 0.22 microfarad.

Condenser 40' 68 micromicrofarads.

Condenser 47 0.22 microfarad.

Condenser 80 About 3 micromicrofarads.

+B- 250 volts.

Tubes 30 and 50 n Type 12AU7. I

Rectifier device Type IN34A germanium crystal.

Periodic potential applied to terminals 26, 26 About 45 volts peak-to- 7 peak.

Peak periodic potential appliedto anode of tube 30- Duration of potential applied to anode of tube 30,

' While' there has been described what is at present consideredto be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various }changesand modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true-spirit and scope of the invention.

-Whatis claimed is.

1. A highly noise-immune synchronizing-signal separator system for a television receiver comprising: first means for supplying a negatively modulated television signal including picture-signal components and synchronizing pulses which tend to be accompanied by unwanted noise signals greater in amplitude than the synchronizing pulses; second means coupled to said first means for developing a potential representative of and which varies dynamically with the amplitude of said synchronizing pulses; synchronizing-signal separating *means responsive to .said first means and'dynamical ly About 350 volts.

About 7 /2 microseconds.

v responsive to said potential for separating said syndom pulses'having an amplitude greater than-that of the 75 chronizing pulses above the maximum level of said picture signal components 'regardlessloii variations in; the ampli f tude of said synchronizing pulses; and means coupled toTsaid first and secondmeanslifor renderingsaidgseparating rator system for a television receiver comprising: first means for supplying a negatively modulated television signal including picture signal components and synchronizing pulses which tend 'to be accompanied by unwanted noise signals greater in amplitude than the synchronizing pulses; second means coupled to said first means for developingta potential representative of and which varies dynamically with theiamplitude of said synchronizing pulses; synchronizing-signal separating means responsiye to said first means, and dynamically responsive to i'said potential for separating said synchronizing pulses above the. maximum level of said picturesignal components regardless of variations'in the amplitude of said 'synchr'oniiiugfpulses; means coupled to said first. and second:'meansr forcrenderingfsaid-sepameans inoperative in responsefto't 6 u'rrenc e ofsaid noise signalsi and meansresponsijvetto sald second t I l H means inoperative, in. response; to the occurence t a of said noise signal s.

, 2. A highly noise-immune synchronizing s1gnal sepaur omp nent; sync oni ing-s nal co p ent and ra'ndom noise pulses having' an a'rnplitude exceeding' 'the peak amplitude of said synchronizing compo nents, and means including a gating circuit for applying sive to current throughsaid rectifier device produced by a said noise pulses, for limiting the magnitude thereof; synchronizing-signalstripper means responsive .to at least some of said components of said video-frequency signal and undesirably responsive to said noise pulses for deriving said synchronizingsignal components; a circuit element 'coupled'to said systemtand having a threshold response and, abovethe threshold, responsive jointly to said noise pulses and said unidirectional potential for means for maintaining the ampiaudeqor saidilsynchronizl- "ingpulses" within airelatively narrowrange for a range of intensities o f said television signal. I I t '3. A noise-suppression apparatus for a television receiver including a supply circuit for, a composite videofrequency signal including a direct-current component and picture components interspersed with synchronizingsignal components and subject to random'nois'e pulses having amplitudes substantially greater than said synchronizing-signal components comprising: a means coupled to said supply circuit, responsive to said signal, andh'aving a point therein for developing at saidpointaunidirectional potential which is representative of andvaries dynamically :with the amplitude of a series of said synchronizing-signal components; a circuit element coupled to said supply'circuit and said "point and having a threshold response and, above the threshold, responsive jointly to said noise pulses and-said'unidirectional potential for developing outpu't pulses therefrom; a synchronizingsignal stripper responsive to at least some of said components of said video-frequency signal'andundesirablyresponsive to said noise pulses for deriving said synchronizing-signal componentsyandmeans for impressing said output pulses on said stripper in opposition to said noise pulses effectively to suppress the latte'rQ 4. In a television receiver, a synchronizing-signal separating aparatus comprising: a synchronously controlled rectifier system, a circuit for'applying to'said'system a composite video-frequency signal including the directsive to said noise pulses for deriving said synehronining' signal components; a circuit elementtcoupled to said;sys tent and having a threshold response and, above rthe threshold, responsive jointly to said noise pulses and said unidirectional potential for developing output pulsestherefrom; and means for impressing. saidoutputpulses on said stripper'means in opposition to said noisepulses effectively to suppress the latter;v ii

5. in a television receiver, a synchronizing-sig al'separating apparatus comprisingi a synchronously controlled rectifier, system, a circuit for applying to saidlsystem a assas in. nee uen n l inge ti hs 'dirsa I latter.

developing outputpulses therefrom; and means for pressing said output pulses on}said stripepr means in oppositionto said npise pulses effectively to suppress the 6. In a television receiver, a synchronizing-signal separating apparatus comprisingra synchronously controlled rectifier system, including a first rectifier device having a cathode, a circuit for applying 'to said deviceja com posite modulation signal including the original unidirectional component, line-synchronizing signal pulses, and random noise pulses having an amplitude exceeding the peak amplitude of said synchronizing pulses an impedance network connected as a cathode load forsaid device and including a point thereon remote from said cathode maintained at a fixed reference potential and having, a time constant at least several times the period of said line-synchronizing pulses and dynamically responsive to the cathode current of said device for deriving a control potential normally maintaining said device in a nonconductivet condition, and means including a gating circuit for applying to said device control pulses in coincident relation with-said synchronizing pulses and with such polarity in relation thereto as to derive across said network during said coincidence said control potential representative of and varying dynamically with the peak amplitudes of said synchronizing pulses; synchronizing-signal stripper means coupledto said network and responsive to said control potential and said composite signal for deriving therefrom linesynchronizing pulses which may include a t-least someof said random pulses; and means including a second rectifier device having an anode coupled to said firstmentioned circuit and a cathode coupled to said impedance network and responsive jointly to said noise pulses and said control potential for deriving and applying to said stripper means output pulses in oppositionto' said noise pulses, whereby the derived line-synchronizing .pulses are sub stantially free from said random pulses.

7. In a television receiver, a synchronizing-signal separating apparatus comprising: 'a synchronously controlled rectifier system, including a first rectifier device having a cathode, a circuit for applying to said device acornposite modulation signal including the original unidirectional component, synchronizing-signal pulses, andrandom noise pulseshaving an amplitude exceeding the peak amplitude of said synchronizing pulses, an irnpedance network connected as a cathode l'oadfor said-device, including a point thereon remote, from said cathode maintained at afixed reference potential, havinga time constant at least several times the period ofsaid synchronizing pulses, anddynamically responsive. to the'cathode current of said device for deriving a, control potential normally maintaining said devicein a nonconductive condition, and means including-a gatingcircuit for applying to said device coritrolpulses in coincident relat ion W t -sai yn roniz n p s n h, uch, p la i yr relation thereto as to derive during said coincidence said control potential which is representative of and varies dynamically with the peak amplitudes of said synchronizing pulses; synchronizing-signal stripper means includ ing an electron-discharge device having an input circuit and an output circuit, said input circuit being coupled to said applying circuit and said network and responsive to said control potential and said composite signal for deriving therefrom in said output circuit synchronizing pulses which may include at least some of said random pulses; and means including a second rectifier device coupled to said applying circuit and said network and responsive jointly to said noise pulses and said control potential for deriving and applying to said stripper means output pulses in opposition to said noise pulses, whereby the derived synchronizing pulses are substantially free from said random pulses.

8. In a television receiver, a synchronizing-signal separating apparatus comprising: a synchronously controlled rectifier system, including a first rectifier device having a cathode, a circuit for applying to said device a composite modulation signal including the original unidirectional component, synchronizing-signal pulses, and random noise pulses having an amplitude exceedingthe peak amplitude of said synchronizing pulses, an impedance network connected as a cathode load for said device, including a point thereon remote from said cathode maintained at a fixed reference potential, having a time constant at least several times the period of said synchronizing pulses, and dynamically responsive to the cathode current of said device for deriving a control potential normally maintaining said device m a nonconductive condition, and means including a gating circuit for applying to said device control pulses in coincident relation with said synchronizing pulses, and with such polarity in relation thereto as to derive during said coincidence said control potential which is representative of and varies dynamically with the peak amplitudes of said synchronizing pulses; synchronizing-signal stripper means including a triode having an input circuit and an output circuit, said input circuit being coupled to said applying circuit and said network and responsive to said control potential and said composite signal for deriving therefrom in said output circuit synchronizing pulses which may include at least some of said random pulses; and means including a second rectifier device coupled to said applying circuit and said network and responsive jointly to said noise pulses and said control potential for deriving and applying to said stripper means output pulses in opposition to said noise pulses, whereby the derived synchronizing pulses are substantially free from said random pulses.

9. In a television receiver, a synchronizing-signal separating apparatus comprising: an electron-discharge means having input electrodes including a control electrode and a cathode and output electrodes elfectively including an anode and said cathode; a circuit coupled to said input electrodes for applying thereto a composite modulation signal, the amplitude of which may vary and which includes the original unidirectional component, and undesired random noise pulses and synchronizing-signal pulses having such polarity as to tend to render said means conductive; an impedance network, connected as a cathode load for said means and including a point thereon remote from said cathode maintained at a fixed reference potential, having a time constant at least several times the period of said synchronizing pulsesand responsive to electron discharges between said output electrodes for deriving a control potential normally maintaining said means in a nonconductive condition; a circuit including a direct-current path connected between said anode and said fixed reference point; a source of a control signal having an amplitude substantially unaffected by amplitude variations of said synchronizing pulses coupled to said output electrodes for supplyingtsaid control signal thereto in synchronous relation with said synchronizing pulses and with such polarity asto develop said discharges and render said means conductive substantially only during the coincidence of said synchronizing pulses and said control signal, thereby to develop across said network said control potential having a value related to the peak amplitude of said synchronizing pulses but substantially independent of said undesired noise pulses; a synchronizingsignal stripper including an electron-discharge device coupled to said applying circuit and to said network at a point other than said fixed reference point, said device having a load impedance and being so poled as normally to be maintained in a nonconductive condition by said control potential but to be rendered conductive by said synchronizing pulses for deriving across said load impedance synchronizing pulses and said noise pulses; and an electron-discharge element connected to said firstmentioned circuit and to said network and having a threshold response and, above the threshold, actuated differentially by said noise pulses and said control potential for developing output pulses therefrom and for impressing said output pulses on said stripper in opposition to said noise pulses effectively to suppress the latter.

10. In a television receiver, an automatic-gain-control and synchronizing-signal separating apparatus comprising: a synchronously controlled rectifier system, including a first rectifier device having an anode and a cathode, a circuit for applying to said device a composite modulation signal including the original unidirectional component, synchronizing-signal pulses, and random noise pulses having an amplitude exceeding the peak amplitude of said synchronizing pulses, first and second integrating networks having time constants at least several times the period of said synchronizing-signal pulses and coupled between said anode and said cathode and including a point common to said networks maintained at a fixed reference potential, said first network being dynamically responsive to the cathode current of said device for deriving a first control potential normally maintaining said device in a nonconductive condition, and a gating circuit for applying to said device control pulses in coincident relation with said synchronizing pulses and with such polarity in relation thereto as to derive across said first network said first control potential and across said second network a second control potential both of which are representative of and vary dynamically with the peak amplitudes of said synchronizing pulses; synchronizing-signal stripper means coupled to said system and responsive to said first control potential and said composite signal for deriving therefrom synchronizing pulses which may include at least some of said random pulses; means including a second rectifier device coupled to said system and responsive jointly to said noise pulses and said first control potential for deriving and applying to said stripper means output pulses in opposition to said noise pulses, whereby the derived synchronizing pulses are substantially free from said random pulses; and a gain-control circuit coupled to said second network for applying said second control potential to said receiver to control the operation thereof.

No references cited. 

